Unsaturated polyester resin compositions containing gelling agents, or gellants, are well-known. For example, in the preparation of glass fibre laminates using unsaturated polyester resins as the bonding agent, it is known to use thixotropic gelling agents which permit easy mixing and spraying of the resins at high shear rates but which greatly increase the viscosity of the resins at low shear rates thus inhibiting the drainage of the resins on vertical surfaces. One of the most effective gelling agents for unsaturated polyester resins is a silica aerogel which is typically added to a solution of the resin in an unsaturated aromatic monomer, such as styrene, at a level of about 1% by weight, based on the weight of the solution. However, silica aerogels are extremely fine and very expensive and, because of their low bulk density, present storage and handling problems and constitute a health hazard.
Various attempts have been made to use organoclays as gelling agents for unsaturated polyester resins, which organoclays are generally smectite clays, e.g. montmorillonite, bentonite, hectorite or the like, at least part of the exchangeable cations of which are replaced by quaternary ammonium cations containing at least one alkyl group having from 10 to 24 carbon atoms.